The present invention relates generally to apparatus and methods for treatment of blood vessels using cooling. More particularly, the invention provides systems, devices, and methods for cryogenically treating a lesion within a patient's vasculature while controlling the pressure state of a cooling balloon.
A number of percutaneous intravascular procedures have been developed for treating atherosclerotic disease in a patient's vasculature. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). PTA employs a catheter having an expansible distal end, usually in the form of an inflatable balloon, to dilate a stenotic region in the vasculature to restore adequate blood flow beyond the stenosis. Other procedures for opening stenotic regions include directional atherectomy, rotational atherectomy, laser angioplasty, stents and the like. While these procedures, particularly PTA and stenting, have gained wide acceptance, they continue to suffer from the subsequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery following an initially successful angioplasty or other primary treatment. Restenosis typically occurs within weeks or months of the primary procedure, and may affect up to 50% of all angioplasty patients to some extent. Restenosis results at least in part from smooth muscle cell proliferation in response to the injury caused by the primary treatment. This cell proliferation is referred to as “hyperplasia.” Blood vessels in which significant restenosis occurs will typically require further treatment.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation, the administration of anti-thrombotic drugs following the primary treatment, stenting of the region following the primary treatment, and the like. While these proposals have enjoyed varying levels of success, not one of these procedures is proven to be entirely successful in avoiding all occurrences of restenosis and hyperplasia.
It has recently been proposed to prevent or slow reclosure of a lesion following angioplasty by remodeling the lesion using a combination of dilation and cryogenic cooling. Co-pending U.S. patent application Ser. No. 09/203,011, filed Dec. 1, 1998 now U.S. Pat. No. 6,355,029, the full disclosure of which is incorporated herein by reference, describes an exemplary stmcture and method for inhibiting restenosis using a cryogenically cooled balloon. While these proposals show great promise for endovascular use, the described structures and methods for carrying out endovascular cryogenic cooling would benefit from still further improvements. In particular, work in connection with the present invention indicates that accurate control over balloon temperature, balloon inflation pressure, and the process of going from an uninflated balloon to an inflated cooling balloon may provide improved results. In general, enhanced control over temperatures, pressures, and the balloon inflation before or aller process during cryogenic cooling would be advantageous.
For these reasons, it would be desirable to provide improved devices, systems, and methods for cryogenic cooling of blood vessels and other body lumens. It would be particularly desirable if these improved devices, systems, and methods were capable of delivering treatment in a very controlled manner so as to limit injury of the adjacent tissues.